1. Field of the Invention
The present invention relates to a USB power supply, especially for charging mobile telephones, which has an automated reduction of power consumption in no-load condition. The invention also relates to a method for controlling the power consumption of a USB power supply.
2. Prior Art
Increasing awareness of electrical energy waste has raised objections against power supplies drawing electrical current even when not in use while plugged into electrical wall socket. The unintended no-load electricity consumption has received names such as phantom load or vampire load.
One of the groups of devices having increased attention are telephone chargers, which are typically left plugged into the electrical wall socket and which draw current even when not charging.
There has been industry wide initiative to reduce the energy wastage by mobile phone chargers due to no-load consumption. GSMA is leading the initiative with his Universal Charging Solution (USC). The GSMA recommends that the power supply, for example charger, must have a 4-star or higher no-load energy rating. In other words, the charger must achieve a no-load consumption <0.15 W.
Techniques for reducing no-load power consumption have been proposed in US patent application US2010/0201208 by Berghegger et al. In this case, the utility includes a controllable switch that is operative to decouple circuitry of the power device from a power source under certain no-load conditions. In one embodiment, the utility provides a switch control module that is operative to sense when an electronic device is coupled to the power device, and in response, to control the switch to couple the power device to the power source. The switch control module may also be operative to detect a condition when the electronic device is no longer drawing power from the power device, and in response, to control the electronically activated switch to decouple the power device from the power source.
Although the power device of US2010/0201208 reduces the power consumption in no-load condition, it does not provide a solution to stop the energy wastage completely, because it has no-load power consumption due to leak currents (page 3 left column first line).
An attempt for reducing the power consumption is found in Chinese patent document CN201142473 by WEI LIU discloses a USB power supply with a mechanical switch that breaks the AC circuit upon manual removal of the USB plug. How-ever, this requires awareness of the user to actually remove the USB plug from the socket, which is in contrast to the behavior of most users to only remove the electronic device from the other end of the cable and let the cable stay in the USB socket. Such behavior does not eliminate the vampire power consumption. Also, there is a substantial risk that the user lets the electronic device to be charged be connected to the USB cable and socket for longer than necessary, i.e. even after the electronic device is fully charged. Having typical behavior from users in mind, this attempt does not provide a proper solution.
Chinese utility model CN201562841U by INVENTEC CORP discloses a USB connector, for example in desktop computers or laptops, comprising an ejector with electromagnets that initiate ejection of the USB plug, for example from a USB data storage device, when the computer or laptop is turned off. The ejection prevents the user from forgetting to disconnect the data storage device in the computer. For further reminding the user not to forget disconnecting the USB connection to the USB plug, there may be provided a dialog box on the computer interface for indicating to the user that the USB should be pulled out when finished. Also in this case, the ejection of the USB cable requires action from the user, namely a response to the dialog box in the user interface or a powering off of the terminal. Power saving is not the issue of this disclosure.
Other disclosures are found in US2008/0007212 (THEYTAZ), CN 100536249 (HUAQI INFORM DIGIT SCIENCE), CN201413914Y (UNIV WENZHOU), WO2008/065659 (WALLETEX MICROELECTRONICS), US6062883 (SCHREIBER), US2008/0185991 (HARRIS).
FIGS. 1A and 1B illustrate two types of prior art sockets with USB power source as described in this introduction.
It would be desirable to have a device that eliminates vampire loads in USB chargers without requiring intervention by the user when the charging of a battery comes to an end.
Another disadvantage in connection with typical telephone chargers is the fact that they take up a wall socket for the connector of the charger, since they are often left in the wall socket even when not in use for charging. For this reason, different solutions have been proposed, namely USB in-wall sockets, for example as published in Chinese utility model CN201178217Y and reproduced in FIG. 1a or even as part of the multiple sockets in extension leads, as illustrated in FIG. 1b for a German type socket.